Had same problem, Fixed it
I had the same problem 3 weeks ago.
I would drive car for about 10 min. Stop then see green stuff leaking from bottom of car. Car never overheated. Added more coolant, added to overflow tank to the correct level. Drive car same problem. Leak appear to be around overflow tank. I could drive for hours, the car never overheated. The only problem was the coolant was always low in the overflow tank. The coolant low level light never came on either.
One day I took out radiator and had it checked. The radiator had a metal core with plastic sides. All connected together with a rubber gasket. My radiator was warpped. Under certain pressure the radiator would leak at the rubber gasket between the plastic housing and metal core. The plastic was bowed outward due to time, excessive heat, who-knows....
The leak would go away once the car cools off, or the pressure is relieved, or the coolant goes down to a certain level within the radiator. Strange problem I never seem before.
I changed radiator, problem is gone, I hope this helps.